Experimental and Computational Study of Transition Metal Doped Zinc Oxide.

Abstract

Pristine and transition metal (Fe, Mn, Co and Ni) doped ZnO powders were synthesised us- ing a hydrothermal method, and characterised by x-ray powder diffraction, ultraviolet-visible absorption spectroscopy, and photoluminescence (PL) emission spectroscopy. Synthesis was carried out at pH 3 and pH 5, and the powders annealed at 280 ◦C and 600 ◦C. Doping was done at concentrations of 1, 2, 4 and 8 mol %. Computational studies were also carried out on undoped and transition metal (Fe, Mn, Co and Ni) doped ZnO using the Generalized gradient Approximation (GGA) of the Density Functional Theory (DFT) implemented in the ab-initio computational suite, Quantum ESPRESSO. Doping was done at concentrations of 5.56 % and 11.11 %. X-ray diffraction spectra showed the presence of secondary phases of Fe3O4, Co3O4, Mn3O4, and NiO at higher doping concentrations. However, the results indicated that synthesis at higher pH diminished the occurrence of these secondary phases. In the experimental work, the band gap energies from the absorption edge of the ultraviolet-visible absorption spectra de- creased with doping concentration for all dopants except for nickel. The band gap energy from the near band edge of the PL spectra on the other increased. The computational results and the experimental results both showed that the band energy in- creased with doping concentration. The unit cell volume also increased for iron and manganese doping in both the experimental and computational results. However, while the computational results predicted a narrowing in the unit cell volume for cobalt and nicked doping, the experi- mental results showed an increase for co